Use semver version for dependencies.

[jaudiger]

I prefer the usage of semver as version constraining for crates. Since they can relax a bit the usage of dependencies in project using this crate.

[nickelc]

Caret requirements are the default strategy, ^1.2.3 is exactly equivalent to 1.2.3.

[jaudiger]

Right. I removed the caret syntax.

For further reference (https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html):

1.2.3  :=  >=1.2.3, <2.0.0
1.2    :=  >=1.2.0, <2.0.0
1      :=  >=1.0.0, <2.0.0
0.2.3  :=  >=0.2.3, <0.3.0
0.2    :=  >=0.2.0, <0.3.0
0.0.3  :=  >=0.0.3, <0.0.4
0.0    :=  >=0.0.0, <0.1.0
0      :=  >=0.0.0, <1.0.0

[jaudiger]

The CI is now green. This PR is ready to be reviewed @fdncred

[sholderbach]

As I said in nushell/nushell#8407 this can be an actively bad practice.
The version range specified for a dependency by Cargo.toml should have as a lower bound a known validated version that satisfies all requirements of what this library depends on.
For the upper bound it would be great if it is semver compatible with the most recent version.
Furthermore in the range of versions between the lower and upper bound there shouldn't be a known bug in non-yanked releases for the features we use.

In the dependency tree of someone consuming our library there could be someone pinning to an exact version that is not satisfying our requirements (if not precisely specified) but allowed by relaxed version specifiers leading to a broken build instead of - in this case necessary - dependency duplication.

For an in depth discussion of the problem of minimal version a timely discussion in Jon Gjengset's video on good crate stewardship: https://www.youtube.com/watch?v=xUH-4y92jPg&t=1476s

cc @fdncred

[jaudiger]

@sholderbach Thanks for your in depth explanation! I already saw a few videos from Jon Gjengset, I will watch your suggestion tonight. Anyway, in order, to not introduce bad practices, and to not create a nightmare for people using this library, I'll close this PR.